Pump



June 14, 1960 E. v. msuus 2,940,395

PUMP

Filed March 13, 1959 2 Sheets-Sheet 1 L0 N m INVENTOR lkk k EdwV-Misu'lis mmlmlu .1 Wk

ATTORNEYS June 14, 1960 E. v. MISULIS PUMP 2 Sheets-Sheet 2 Filed March13, 1959 INVENTOR E dwardV MisuLi-s ATTORNEYS 2,940,396 Patented June14, 1960 PUMP Edward V. Misulis, Watertown, N.Y., assignor to The giewYork Air Brake Company, a corporation of New ersey Fiied Mar. 13, 1959,Ser. No. 799,257

6 Claims. (Cl. 103-37) This invention relates to variable displacementbydraulic pumps of the reciprocating piston type in which the pistonsare mounted in a stationary cylinder block. More particularly, theinvention is concerned with the mechanism for varying the displacementof such pumps.

Pumps of this type include a rotary drive shaft carrying a cam which isarranged to coact with the pistons and move them on their dischargestrokes in timed sequence, inlet and discharge passages connecting theworking chamber of each piston with the inlet and discharge ports,respectively, and valve means for preventing reverse flow from thedischarge port to the working chambers through the discharge passages.Each inlet passage is connected with one cylinder bore by a port whichis so located as to be overtravelled and closed by the associated pistonduring the discharge stroke of that piston. Because of this, a portionof the fluid displaced by each piston is returned to the inlet port evenduring maximum displacement operation. In a typical case, 60 of eachrevolution of the cam is required to overtravel the inlet port, thushaving only 120 of movement for actual pumping operation. Frequently,these pumps employ a by-pass mechanism which diverts a portion of theoutput of each piston through the pump housing for the purpose ofcooling the housing. Approximately 30 of cam rotation is required toproduce this bypass flow. As a result, only 90 out of the maximum of 180of cam rotation is actually used to discharge pressure fluidfrom thepump. Furthermore, the by-pass flow mentioned above is pro duced evenduring conditions of maximum displacement operation. This reduces theefliciency of the pump unnecessarily because the cooling afiorded by theby-pass flow is required only during conditions of minimum displacementoperation. In those pumps in which the inlet port communicates with thespace in the housing surrounding the cam, the pump can be operated withhigh inlet pressurization only if a positive piston return mechanism isprovided. Spring return devices cannot be employed because the fluidpressure forces acting on opposite ends of each piston at the beginningof the suction stroke are not balanced. Springs of a size suflicient toovercome the fluid pressure unbalance would increase the bearing loadson the cam beyond a tolerable limit.

The object of this invention is to provide an improveddisplacement-varying mechanism for pumps of the type described whichresults in a pump free from the disadvantages just mentioned. Accordingto the invention, the inlet passage leading to each cylinder bore isprovided with an inlet valve which is shiftable between passage-openingand passage-closing positions and which is biased by a spring and by thefluid pressure in the cylinder bore toward the passage-closing position.Each inlet valve is connected with a control motor whose working chamberis in communication with the inlet port and which functions to shift thevalve in the opposite direction during the suction stroke of theassociated piston. The invention provides a control valve which operatesin timed relation with the cam to interrupt communication between theworking chamber of each control motor and the inlet port when theassociated piston reaches a predetermined point in its suction stroke,and to reestablish this communication when that piston reaches a certainposition in its discharge stroke. In the preferred embodiment, thecertain position and the predetermined position are equidistant from thetop deadcenter position so that the displacement-varying mechanismoperates independently of the direction of rotation of the cam.Connected with the control valve is a regulating device. which isefiective to vary the said certain position at which communicationbetween each control motor working chamber and the inlet port isreestablished. When the working chamber of a control motor isdisconnected from the the inlet port, the motor becomes hydraulicallylocked and the pressure in the associated cylinder bore is ineffectiveto close the inlet valve. As a result, fluid displaced by each pistonduring this portion of its discharge stroke returns to the inlet port.When each piston reaches said certain position, communication betweenthe working chamber of the associated control motor and the inlet portis reestablished and the inlet valve closes under the action of thespring and the fluid pressure in the cylinder bore. For the remainingportion of its discharge stroke, the fluid displaced by each piston isdelivered to the discharge port. Since the regulating device governs thetime during each discharge stroke that the associated inlet valve isopen, it will be apparent that the invention serves to vary theefiective displacement of the pump.

The invention also provides by-pass passages, one of which connects eachcylinder bore with a by-pa'ss port. Flow through these by-pass passagesis controlled by a by-pass valve which is normally closed but which isautomatically opened when the control valve is interruptingcommunication between the working chambers of the control motors and theinlet port for a maximum portion of the discharge stroke of the pumppistons.

A pump embodying this invention is superior to its prior counterpartsbecause it utilizes a discharge stroke during conditions of maximumdisplacement operation and because it creates a by-pass flow only duringminimum displacement operation. Furthermore, since the working chambersof the control motors communicate with the inlet port, spring returndevices can be used for the pistons even when the inlet is pressurized asubstantial amount. This is attributable to the fact that the pressurein the inlet port is transmitted to the working chambers of the controlmotors and causes these motors to open the inlet valves and thusequalize the pressures acting on opposite ends of the pistons duringtheir suction strokes.

The preferred embodiment of the invention will now be described indetail with reference to the accompanying drawings, in which:

Fig. 1 is an axial sectional view of a swash plate pump incorporatingthe invention; the control valve being shown in its maximumdisplacement-establishing position.

Fig. 2 is an elevation view of the sleeve of the control valve.

Fig. 3 is a sectional view taken on line 3-3 of Fig. 1.

Fig. 4 is an axial sectional view of the control valve showing therelative positions of the two valving elements in an intermediatedisplacement-establishing position.

Fig. 5 is a sectional view taken on line 5-5 of Fig. 4.

Fig. 6 is a view similar to Fig. 4 but showing the relative positions ofthe two valving elements in the minimum displacement-establishingposition.

Fig. 7 is a sectional view taken on line 7-7 of Fig. 6.

As shown in Figs. 1 and 2, the pump comprises a 4 housing havingseparable sections 1 1 and 12 which are connected together bysholts 13and which are cored and bored to receive and hold a cylinder. block '14.The r 7 cylinder block contains a circular series of nine uniiormlyspaced cylinder'bores 15 for receiving the pistons 16; ;At its; leftend,each piston 16 carries a shoe which is in sliding engagement with theswash plate 18. The pistons are 'rec'ipro'cated 'in the bores 15 the 7action of swash plate 18 and springs19,

The housing section '11 contains an inlet port which communicates withthe cylinder bores'15 through the chamber '22, formed in section .11,and the longitudinal and radial passages 23 and 24 formedin eylinderblock 14. Flow into feach cylinder here is controlled by an inlet valve25. Whose opposite fend faces 27 are subi'ect to the pressure in thecylinder bore and develop in Fig. 1. In this position, edge 48 of land47 has not overtravelled any of the passages 44 so the working chainbers35 of the control motors 34will be in continuous communication withinlet port 21 through passages 36, slots 43, drilled passages 44,plunger groove 45, radial and axial passages 51 and 49, chamber 52,passages 53 and 23, and chamber 22. a piston 16 commences to'move to theleft on its suction stroke, a pressure is produced in bore that is lessthan the'inletpressure in working chamber35 of theassociatedcontrollmotor, and consequently the motor 34 opens the inletvalve against the bias of. spring 28 and the. netpr essu reforcedeveloped .by ,end .faces '26 and21.};"This+allows the fluid entering'inlet' port 21 to new into 'the cylinder bore pressure forces which,togetherwith spring 28 'ahdthe controlin'iotor described below, shiftthe valve in opposite directions'during the suctioh anddiiiehargestrolee s'ot the associated piston 16' fluid under pressure, dls'chargediro'xn each cylindei-boi'e-15, passes through'a check 'valve '29"into the annular .di'sehapge manifold 31 V andisdelivered tothehydfaulic cifc'uit by the discharge "port 32 5 Each inlet Valve 25 carriies asunder-s3 which serves as the piston or a controlrnoftor 34. Theworkingchamher 35 ot each control motor is coniiec'ted by'a passage 7"3-6 with a control valve '37 'whih furictions to v ary the timeduringeach reyoh tioh er swash' late18 that each working ch'amber 35 isin communication with'ililet port 21. -Cont rolfva1ve 37 includes,apaaed'sreevje 38 which reciprocates'in an axial bore formed inthecylinder block rotary valve "plunger--41 which is connected in driven15. As each piston 16' approaches its outermost or bottom dead-centerposition, .thepressure in' bore 15 increases, the spring 28 begins toshift thevalve 25'to the right towardits closed position.,/ When thepiston reaches its bottomdead-center position, the" pressures in. ore 15and workin c'hamber 35'w'ilI have eqnalizedtand the inlet valve will beclosed.' fA's thefpiston 16 starts to move to the lrighton itsdischargej'stroke', thelpressure in. bore 15will' rise abovefthat'in,workingjchamber 35, withgthe result that the nefpressure force developedby end faces 26" and 21' will exceed the ierce cxer tedby controlmotori34, The Idiifererice between the net pressure force, and the forcedevelopedfby motor 34 will aidspfin as in holding the inlet'valve25iiiits clesed but which'is prevented from rotathig by a pin 39,and a a relation with swash plate 18 'by splined coupling shaft 42. Theouter-periphery of sleeve 38 containsa s eries of nine uniformly spacedlongitudinal slots 43, each ofwhich communicates with one of thepassages 36 and is connected with 'the interior or the sleeve byadrilled V radial passage 44. The rotary plunger 41 is formed with anannular groove 45 which defines two spaced valve lands 46 and 47; theleft edge 48 of land 47 lying in ,a plane which is inclined relativelyto the axis of the plunger. Axial andradial passages 49 'and 51,"formedin plim'g'en41, connect m ma/e 45 with the chamber 52 containedin'housingsection 12. chamber isin continuous communication with inletport 21; via passages V ,53 'and23 and chamber 22. Sleeve 38 is biasedto the position shown in Fig.1 bycoil spring 54 and is moved .totheright against this bias by a valve motor 55 having a working chamber,56 and a piston 57 which is defined by a shoulder formed on the outerperiphery of the sleeve. Working chamber 56 communicates with dischargemanifold 31 through passage 58 and conduit formed in restrictor plug'59.

The cylinder block 14"a1so contains a plurality-of radial passages 61which connect the cylinder bores 15 with a by-pass valve carried bycontrol valve sleeve 38,

The by-pass valve includes a land 62 and a groove 63 a restricted"formed in sleeve 38; the land 62 normally closing the passages 61. .Thegroove 63'is so dimensioned and located that, when the sleeve 381's inits minimum displace- V mom-establishing position '(see Fig. 6.), itconnects the passages 61 with the. by-pass port 64 through the passage65. The connection between each passage Gland cylinder bore 15is so.located that it is overtravelled and sealed by the inlet valve 25 whenthis valve isopen. This arrangement prevents-reverseflow from passages61 ation.

' to cylinder; bores. 15. during;r'ninimurn. displacement oper- EOperation;

' When the pump is'running and discharge pressure-in manifold 31islbelow a predetermined value, termed the reference value, the forcedeveloped by valve motor 55 :is insuflicient to overcome the bias of;spring 54. and control valve sleeve 38 will take up the 'posit'ior'ivshown '48" uncove p s a e; eiflqifl position. As a result, all of thefluid displaced by piston 16 during its discharge stroke will passthrough check valve 29 and manifold 31 and discharge through port 32.

Iffiischaf'ge pressure'shou'ld rise above the, ieferen ce value (byreason of a decrease. in the demand for hy-. 'draulic'fluid), valvemotor 55 will shift sleeve 38't'o the right against the bia or spring 54to a position inwhich the' for'ces' developed by this spring and motorare balance- 1 and. the edge tsha's everaa'vened same of the passages44-. Such a 'posit'iohfis shownr in Fig. 4. vAn

inspection of'tbjs figure and Fig. 5 will show that'dui'ing one-halffofeach revolution of swash plate 18 Ge, during one-half of one completepumping cycle of each piston 16), land '47 iotary plunger! 4liaterruptscommunication between each passage 36, aifd inlet port 21. Because ofthe tactttiat the angular position of each slot 43, about the axis ofthe cylinder barriehis the a as to e cylinder berels' with which it isassociated, and because of the. p aerela't-ions'hip between edge 48 andswash plfat'eltl, this interruptioh occurs atithe mid-point of thesuctionvstr'oke of each. piston 16. and

continues. until the rpiston rcaches the. midpoint of its 1 dischargestroke. Consequently','when each piston 1.6 begins to move on itssuction stroke, the working chartiber 35 of theassociated control motor34will be in communication with the inlet port 21, ai'idlthe, pressuredifferential between this chamber and the" cylinder-bore 15 will openthe inlet Valve 25. and allb v v' fluid. to new into the cylinder bore.When a piston 16' reaches the mid-point of its stroke and .the edge 48or the rotary plunger. 41 overlaps the corresponding passage 44,, theassociated control motor 34 becomes hydraulically locked.

This when thatpiston 16 passes itsbojttom' 'dead center position andcommences to; move pn its discharge stroke, spring ZS' andthe: pressure;in. 'cylinder bore 15 close the;ii1let valve; 2 51 'an'cl'the"pistonwill discharge past thisjva sage'24fand longitudinal passa'ge ZSLV '16jrea'ches the mid-point offit's idis'bhar'g e stroke andedge Ithat. the. efiec'tive, displacement lo'f when the et -va iws.ea ;ef e tqa e s-h 9 th displacement established by this valve when it is in theFig. 1 position.

a When the discharge pressure rises to the predetermined maximum, valvemotor 55 shifts the sleeve 38 to the minimum displacement-establishingposition of Fig. 6 in which the valve land 47 covers each passage 44 forall but a small portion of each revolution of swash plate 18. As thesleeve 38 reaches this position, the annular groove 63 of the by-passvalve overtravels the passages 61 and thus establishes communicationbetween each cylinder bore 15 and the by-pass port 64. As a result, thefluid displaced by each piston 16, during the short time that theassociated inlet valve 25 is closed, will be discharged under lowpressure through the by-pass port 64. This small by-pass flow serves tocool the pump during the time that the demand for hydraulic oil in thecircuit supplied by discharge port 32 is a minimum. Since this flowoccurs at a low pressure, little power is required for this purpose.

Although only three positions of the sleeve 38 have been illustrated anddescribed, it will be apparent that control valve 37 effects aprogressive variation in displacement as the discharge pressure variesbetween the reference value and the predetermined maximum value. If thespring 54 has a constant rate, the relationship between effectivedisplacement and discharge pressure will be substantially linear.

It will also be apparent that since the distance sleeve 38 moves intravelling between its minimum and maximum displacement-establishingpositions is small, spring 54 may have a low rate. This is a desirablefeature because it afiords a small control pressure difierential, i.e.,the differential in discharge pressure required to shift sleeve 38between its limiting displacement-establishing positions is small.

As discharge pressure decreases below the predetermined maximum, theforce exerted by valve motor 55 also decreases and spring 54 shifts thesleeve 38 to the left to thereby interrupt the by-pass flow to port 64and progressively increase the time during each revolution of swashplate 18 that the working chambers of control motors 34 are incommunication with the inlet port 21. When the discharge pressure againequals the reference value, the sleeve 38 will be in its Fig. 1 positionand the effective displacement of the pump will be a maximum.

It should be observed that the pressure prevailing at inlet port 21 hasno adverse effect on the basic operation of this pump even thoughsprings are used to move the pistons on their suction strokes. This isattributable to the fact that the working chamber of each control motor34 is always in communication with the inlet port at the beginning ofthe suction stroke of the associated piston 16, and therefore high inletpressures actually aid opening of the inlet valves. Once open, thesevalves remain open for the balance of the suction stroke and therefore,the fluid pressure forces acting on opposite ends of pistons 16 arebalanced during the entire suction stroke and the return function ofsprings 19 is not impaired.

It should also be noted that in the illustrated embodiment, the rotaryplunger 41, and particularly the edge 48, is symmetrical about avertical axis as viewed in Figs. 3, 5 and 7. As a result, during partialdisplacement conditions (i.e., when sleeve 38 is in a position otherthan the one shown in Fig. 1), the point in the suction stroke of eachpiston 16 at which edge 48 overtravels the associated passage 44 is thesame distance from the top deadcenter position as the point in thedischarge stroke at which this passage is reopened. This is a desirablefeature because it renders the operation of the displacement-controllingmechanism independent of the direction of rotation of swash plate 18.

As stated previously, the drawings and description relate only to apreferred embodiment of the invention. Since many changes can be made inthe structure of this d embodiment without departing from the inventiveconcept, the following claims should provide the sole meas me of thescope of the invention.

What is claimed is:

1. In a pump including inlet and discharge ports, a stationary cylinderblock containing a plurality of cylinder bores, a piston reciprocable ineach bore and defining therewith a working chamber whose volume isvaried by the motion of the piston, a rotary drive shaft carrying a camwhich is arranged to coact with the pistons and move them on theirdischarge strokes in timed sequence, inlet and discharge passagesconnecting each working chamber with the inlet and discharge ports,

respectively, and valve means for preventing reverse flow from thedischarge port to the working chambers through the discharge passages,the improvement which comprises inlet valves, one located in each inletpassage and each being shiftable between passage-opening andpassage-closing positions; means responsive to the pressure in eachcylinder bore for urging the associated inlet valve toward itspassage-closing position; resilient means biasing each inlet valvetoward its passage-closing position; control motors, each having aworking chamber and a movable element subject to the pressure in thatchamber and connected with one inlet valve for moving that valve towardits passage-opening position against the bias of the pressure responsivemeans and the resilient means; a motor passage connecting each controlmotor working chamber with the inlet port; valve means operable in timedrelation with the cam for closing each motor pas sage when theassociated piston reaches a predetermined position in its suction strokeand for reopening each passage when the associated piston reaches apredetermined tion in its discharge stroke; and regulating meansconnected with the valve means for varying the said certain position atwhich the passages are reopened to thereby vary the effectivedisplacement of the pump.

2. The invention defined in claim 1 in which the said predeterminedposition and the said certain position of each piston are equidistantfrom the top dead-center position; and in which the regulating means iseffective to shift these two positions equal amounts and in the samedirection.

3. In a pump including inlet and discharge ports, a stationary cylinderblock containing a plurality of cylinder bores, a piston reciprocable ineach bore and defining therewith a working chamber whose volume isvaried by the motion of the piston, a rotary drive shaft carrying a camwhich is arranged to coact with the pistons and move them on theirdischarge strokes in timed sequence, inlet and discharge passagesconnecting each working chamber with the inlet and discharge ports,respectively, and valve means for preventing reverse flow from thedischarge port to the working chambers through the discharge passages,the improvement which comprises inlet valves, one located in each inletpassage and each being shiftable between passage-opening andpassageclosing positions; means responsive to the pressure in eachcylinder bore for urging the associated inlet valve toward itspassage-closing position; resilient means biasing each inlet valvetoward its passage-closing position; control motors, each having aworking chamber and a movable element subject to the pressure in thatchamber and connected with one inlet valve for moving that valve towardits passage-opening position; a motor passage connected with eachcontrol motor working chamber; a common passage connecting the motorpassages with the inlet port; a control valve located at the junction ofthe motor passages and the common passage and having two coaxial valvingelements which are arranged for relative rotational and longitudinalmovement, one of the elements being formed with a circular series ofports,

here being one port connected with each motor passage,

and the other element carrying a control edge which is so shaped thatrelative longitudinal movement between the twovalving elements in onedirection causes a pro-.

gressively increasing number of ports to be overtravelled by the edge,said other. element interrupting communication between a port and thecommon passage when the edge overtravels'that portymeans biasing one ofthe valving elements in the longitudinal direction toward a V positionin which the control edge overtravels a minimum 'number of ports; avalve motor for shifting said one v'alving element in the oppositedirection against the biasing'means to a position in which the controledge overtravels a maximumnumber of'ports; and means forma ing a drivingconnection between the jdriveishaftand one ot the yalving'elementsfortprodu'cing relative rotation between the ports and the controledge-in timed relation with the movement of the pump pistons, the partsbeing so arranged that said relative rotational movement causes eachportto be overtravelled during the suction stroke 7 of its associated pistonand reopened during the discharge stroke ofthat piston. i

The invention defined in claim -3 which includes a by-pass port;by-passpassages connecting the by-pass port with each of the working chambersof the pump pistons; a by-pass valve normally closing the by-pass passages; and means operatively connecting the by-pass valve and the valvemotor, whereby when said one valving element of the control valve. is inthe positionvin whichthe maximum number of portsare overtravelled theby-pass' valve is open, and when that control valve element is in'theposition in which the minimum number; of ports.

are overtravelled the by-pass valve is closed.fij v 5. The inventiondefined in claim-iinflWhich the parts are so selected and arranged thatthe distanceeach pistontravels between the point at which 'theassociatedcontrol valve port is overtravelled and the bottomdead-centei' positionis the same as the distance that piston travels between the bottomdea'd-center position vand the point at which that port is reopened. H a

6; The invention defined in claim 4 in which flow through each by-passpassage is also controlled by one of the inlet valves," the parts beingso arranged that each inlet"valve opens and closestheassociated by-passand inlet passages in reversesenses.

' References Cited in the file of this patent UNITED STATES PATENTSGreat Britain e t ,Nov. 3', 1937 UNITED STATES PATENT OFFICE vCERTIFICATE OF CORRECTION Patent No, 2 94O 396 June 14 1960 Edward V..Mi sulis inted specification It is hereby certified that error appearsin the pr said Letters of the above numbered patent requiring correctionand that the Patent should read as corrected below.

Column e line 33 for "predetermined' line 34 for "tion read me positionsa 73 for "here" read rm there read we certain me column 6 line Signedand sealed this 1st day of November 1960.

( S EAL) Attest:

KARL Axum ROBERT C. WATSON Commissioner of Patents Attesting Oflicer

